Interstitial radiation therapy, a form of brachytherapy, has been performed since the beginning of the 20th Century. Radium was developed by Madam Curie and Alexander Graham Bell proposed the use of radium in tumors. Subsequently, metal needles were developed in which a radium isotope was encapsulated for insertion in close proximity or into tumors. Where the tumor was deep seated, an operation was necessary to provide access to the tumor. Such therapy had serious problems and disadvantages. The high energy of the radium isotope required a great deal of shielding and subjected the personnel to harmful exposure. In addition, the needles tended to break as they aged resulting in the release of the radioactive contents. Since the radium isotopes had a half-life of about 1600 years, they produced an extreme contamination hazard.
Thus, efforts have been made to develop more effective brachytherapy which is safer and more convenient to use. This has resulted in the development of radioactive materials that have lower energies and thus require less shielding and have shorter half-lives to reduce the risk of contamination. Thus, permanent seeds of encapsulated radon-222 having an energy level of 0.78 MEV and a half-life of 33.83 days or of encapsulated gold-198 having an energy level of 0.42 MEV and a half-life of 2.7 days have been used. More recently small seeds of iridium-192 having an energy level of 0.30 MEV and a half-life of 74.2 days and iodine-125 having an energy level of 0.028 MEV and a half-life of 60 days have been developed. Such seeds are shown, for example, in U.S. Pat. Nos. 3,351,049 and 4,323,055.
Such iridium and iodine seeds are on the order of 4.5 mm in length and 0.8 mm in diameter and are implanted in the tumor or placed on the surface of the tumor. Both of these sources have lower energies than radium that allow for simpler shielding and less radiation exposure to personnel. With seeds of iodine encapsulated in a material such as titanium, shielding is provided by the surrounding tissue and the seeds can be left in the patient permanently without the need for major precautions.
A further development in brachytherapy has been the development of techniques for handling the seeds. In one technique, hollow metal needles are inserted into the tumor and the seeds are thereafter inserted into the needles while the needles are being retracted to deposit the seeds in the tumor. Such devices are shown in U.S. Pat. No. 4,402,308. The most commonly used instruments are the Henschke and Mick devices. The spacing of the needles is determined by a nomograph developed by Drs. H. M. Kuam and L. L. Anderson of the Department of Medical Physics at Memorial Sloan-Kettering Cancer Center, New York, New York. The use of such devices has distinct disadvantages and problems. The overall length of such devices is over 20 cm and they have significant weight making them difficult to manipulate. Since the implant is performed through an open surgical wound, the needles can only be placed straight in a straight line or at an angle dictated by the relationship of the incision to the tumor. For example, the prostate is directly below the pubic bone with the incision being located cephalad. Since the prostate tends to rise behind the bladder, the preferred direction of the implant should be from a caudal approach, but this is not achievable using the available devices.
Another disadvantage of the above technique is that the seeds are deposited in a track made by the needle. When the needle is withdrawn, there is a tendency for the seeds to migrate in that track resulting in a poor distribution of the seeds. Because the energy levels are low (an exposure constant of 0.0184 for iodine-125 vs. 0.825.sup.2 Rm.sup.2 ci.sup.1 h.sup.1 for radium), distribution between centers of adjacent seeds should be on the order of 1 cm. Poor distribution of seeds can result in undesirable concentrations of seeds resulting in either an overdosage or underdosage of radiation.
The seed is small because it needs to fit in small bore needles which minimally change or damage tissue. The seed has a high seed surface dose and is difficult to handle because of its small size and can be easily lost and difficult to label. In addition, the technique of implantation of individual seeds is time consuming.
In another technique for treating tumors, seeds are initially placed by hand in a woven or braided absorbable carrier such as a braided suture. The carrier with the seeds laced therein is then secured in place to form a suitable implant. This technique is time consuming and may necessitate handling of the suture as well as having the same problems as to position and retention as the catheters. In order to minimize the radiation to personnel during handling and shipping, the suture with the seeds placed therein is shielded by placing it in a curved metallic tube. See European Patent Application Publication Number 0 064 860, published 17.11.82, Bulletin 82/46.
In another technique that has been developed for treatment of tumors, plastic catheters are sutured on or in the tumor area and seeds placed in the catheters by insertion of a nylon tube carrying the seeds. After the desired treatment period, the nylon tubes are removed. The catheters are difficult to place so as to provide the proper dose distribution. It is also difficult to accurately space the catheters in parallel array over irregular surfaces and to anchor the catheters to the tissue. Irregular spacing can result in radiation overdose or underdose. Where the ends of the catheters are brought to the surface of the skin and sutured in place, there is an incipient source of contamination.
None of these prior art systems allow for the adequate placement of the seeds in the configuration of the tumor treated.
Accordingly, one of the objectives of the present invention are to provide a delivery system which obviates the aforementioned disadvantages and places and holds the seeds in the desired and accurate position to provide the desired radiation dose.
Another object of the present invention is to provide a delivery system that is safe and easy to use and causes a minimum of trauma to tissue.
Yet another object of the present invention is a delivery system that allows for excellent control of the radiation dosage given the tumor.
In accordance with the invention, the delivery system comprises a conformable sheet of material absorbable in living tissue which has a plurality of radioactive seeds dispersed therein in a predetermined array. In one form, the sheet comprises a continuous flexible film having radioactive seeds encapsulated therein and which sheet may be attached to the surface of a tumor.